write a cuda program to compile both sm_1x and sm_2x - cuda

Question

My problem is very similar to this link, but I am not able to fix it.
I have a CUDA program using cuda layered texture. This feature is only available with Fermi architecture (with compute capability more than or equal to 2.0). If the GPU is not Fermi, I use 3d texture as substitution for layered texture. I use __CUDA_ARCH__ in my code when declaring the texture reference (texture reference needs to be global) as this:
#if __CUDA_ARCH__ >= 200
texture<float, cudaTextureType2DLayered> depthmapsTex;
#else
texture<float, cudaTextureType3D> depthmapsTex;
#endif
The problem I have is that it seems __CUDA_ARCH__ is not defined.
The things I have tried:
1) __CUDA_ARCH__ is able to work correctly within cuda kernel. I know from the NVCC document that __CUDA_ARCH__ is not able to work correctly within host code. I have to define the texture reference as global variable. Does it belong to host code? The extension of the file being compiled is .cu.
2) I have a program that works correctly using layered texture. Then I add __CUDA_ARCH__ macro in two ways:
#ifdef __CUDA_ARCH__
texture<float, cudaTextureType2DLayered> depthmapsTex;
#endif
and
#ifndef __CUDA_ARCH__
texture<float, cudaTextureType2DLayered> depthmapsTex;
#endif
I found neither of them work. Both have the same error. error : identifier "depthmapsTex" is undefined. It looks as if the MACRO __CUDA_ARCH__ is defined and not defined at the same time. I suspect this relates to the fact that the compilation has two stages, and only one of the stage can see __CUDA_ARCH__, but I am not sure what has happened exactly.
I use cmake + visual studio 10 to set up the project and compile the code. I suspect if there is anything wrong here.
I am not sure if I have provided enough information. Any help is appreciated. Thank you!
Edit:
I tried to find any example that uses __CUDA_ARCH__ in Nvidia CUDA SDK 5.0. The following code is extracted from line 20 to line 24 in file GPUHistogram.h in the project grabcutNPP.
#if __CUDA_ARCH__<300
#define PARALLEL_HISTS 64
#else
#define PARALLEL_HISTS 8
#endif
And from line 216 to line 219, it uses the MACRO PARALLEL_HISTS:
int gpuHistogramTempSize(int n_bins)
{
return n_bins * PARALLEL_HISTS * sizeof(int);
}
But I found there is a problem here. PARALLEL_HISTS is not correctly defined. If I change the first clause to #if defined(__CUDA_ARCH__)&& __CUDA_ARCH__<300, I found the CUDA_ARCH is not defined. Does the CUDA SDK example use CUDA_ARCH in the wrong way?

Answer 1

I am not sure I understand the exact problem which may well have an elegant solution. Here is an inelegant brute-force approach I have used in the past. Create two kernels with identical signatures, but different names (e.g. foo_sm10(), foo_sm20(), in two separate .cu files. Compile one file for sm_10, and the other file for sm_20. Move common code that is independent of compute capability into a header file, and include it from both of the previously mentioned .cu files. In the host code, create a function pointer to invoke the architecture-dependent kernels. Initialize the function pointer to the approriate architecture-dependent kernel based on the compute capability detected at runtime.

Answer 2

If you want to figure out the compute capability of your GPU, you could try something like:
int devID;
cudaDeviceProp props;
CUDA_SAFE_CALL( cudaGetDevice(&devID) );
CUDA_SAFE_CALL( cudaGetDeviceProperties(&props, devID) );
float cc;
cc = props.major+props.minor*0.1;
printf("\n:: CC: %.1f",cc);
But I have no idea how to solve your problem.